(1) Field of the Invention
The subject of the present invention is an implantable subcutaneous device that can be positioned anywhere in a living body, directly under the skin of this body to send and/or receive data to or from the outside of said body, such as to at least one other device positioned outside said body.
One of the principal applications of this invention is to create auditory prostheses intended to correct profound deafness of a human being and that comprises electrodes for this purpose either implanted in the cochlea, or extracochlear and positioned on the round or oval window of the cochlea, and designed to send electrical signals to the auditory nerve fibers situated in this cochlea.
(2) Prior Art
Such cochlear implants are known and thus replace deficient cochleas, directly stimulating the auditory nerve as a function of sound captured by an external microphone; this microphone is generally situated in a housing also comprising a microprocessor and a support of the behind-the-ear type for positioning it discretely behind and around the ear.
The sounds thus captured by the microphone are digitized and processed in this external housing, which, by means of a set of antennas (at least one of which is associated with this outer housing, and the other, subcutaneous, with the implant) sends information signals corresponding to these sounds to the implant positioned under the skin.
The implant generally comprises a small housing made of titanium and silicone in order to be biocompatible and positioned surgically under the skin; it bears electronic components and receives the information signals from the external antenna by means of its own antenna and for the intracochlear electrode devices sending it to and over these electrodes that have been positioned in the cochlea; like a piano keyboard, each electrode corresponds to a sound signal frequency band and the auditory nerve endings in contact with the electrodes will send the electric impulses to the brain, which will interpret these signals as sound.
Moreover, such an implant requires a minimum energy, which is provided by means of electromagnetic coupling with coils situated face-to-face in the implantable and external devices, respectively, and kept centered with regard to one another by means of a set of magnets (respectively connected to the implantable and external devices); their yield is certainly low since there is no air gap, but it is sufficient for the small quantity of energy required, as long as the various components are chosen and positioned judiciously. Certain implantable devices also have rechargeable batteries.
Other applications are possible, of course, any time that it is necessary or useful to be able to collect data on an organ by using so-called physiological data collection electrodes, or, in contrast, to send information to this organ (such as the cochlea) from the exterior without permanent perforation of the skin.
Various devices are known and developed by different manufacturers, who have filed various patent applications, such as:                patent EP 999 874 of the ADVANCED BIONICS CORPORATION and ALFRED E. MANN FOUNDATION FOR SCIENTIFIC RESEARCH and entitled “Implantable device with improved feed and battery recharge configuration” filed on Jul. 31, 1998,        patent application EP 1,166,820 filed by Medtronic, Inc. Entitled “Implantable medical device with an external electric recharging coil” filed on Jun. 19, 2000,        or even patent U.S. Pat. No. 6,246,911 of Mr. Peter Seligman filed on Jul. 1, 1999.        
All these manufacturers have performed studies and made compromises in the design of their devices in order to simultaneously satisfy contradictory constraints such as: the necessity for the implants to be biocompatible, the simplest possible implementation for the surgeon, a minimum encumbrance, a sufficient yield both in data transmission and in electric recharging of the implant (low yield, in fact, as a result of the proximity of the receiving/transmitting antennas to the titanium housing, and the poor electromagnetic coupling of the coils for energy transfer), as well as the presence of magnets, which also disrupts MRI imaging, and in that one must be able to act on the body of the patient concerned.
Therefore it is necessary, among other things, to maximally reduce the dimensions of the implantable device both in thickness and in surface, while having the possibility of being able to remove the centering magnet without having to remove the implant, in order to be able to do such imaging.
To do this, currently all manufacturers have chosen the compromise of positioning the antenna part and coil of the implant as well as its magnet in a protective silicone casing and positioning this assembly on the side of a titanium housing containing the electronic part and the connection to the cochlear electrodes; the magnet, which is held in place by the silicone casing, which has a opening, can be removed by a small incision once the implant is in place, and the antenna and the coil, offset from the titanium housing, are less disrupted by this housing and permit a satisfactory yield.
The antenna and the coil can either be separate, or made up of a same component that then assures both data transmission and electromagnetic coupling for energy transfer; in the present description, we designate as a coil any component that permits either only electromagnetic coupling for energy transfer, or assuring both, and even possibly at the same time, this function as well as that of a data transmission antenna.